It is common practice to filter blood and other aqueous liquids by passing them through hydrophobic filter media. Hydrophobic materials, by their very nature, tend to reject aqueous liquids. Accordingly, one problem with use of hydrophobic filter media for the filtration of aqueous liquids is obtaining rapid filtration.
In one blood filtration process, blood to be filtered is introduced to the upstream side of the filter media, and it is desired to have the initial flow of the filtered blood, i.e., breakthrough from the downstream side of the filter media, as soon as possible. The hydrostatic head of blood above the filter media forms the driving force for the blood through the filter, and it is desired to obtain breakthrough with a minimum blood volume above the filter media, i.e., with a minimum hydrostatic head. Unfortunately, hydrophobic filter media resists the initial flow of blood through the media such that, in breakthrough tests, the time delay between the introduction of blood to the upstream side of the media and the initiation of flow through the media is longer than desired.
For industrial applications, a wetting agent can be deposited in the hydrophobic filter media to assist the flow of aqueous liquids through the media. However, the filtration of blood poses many unique problems which prevent the application of industrial wetting agents to the filter media. For example, the wetting agent must produce only minimal hemolysis and have no more than minimal complement activation. It must not induce abnormalities in blood coagulation or in platelet function, and because the filter media must be sterile, it must be compatible with gamma sterilization and ethylene oxide sterilization. The wetting agent must be, under the conditions of use, essentially nontoxic, noncytotoxic and nonpyrogenic, and it must not be a suspected carcinogen. The filter media, after being treated with the wetting agent, must pass United States Pharmacopeia (USP) Class VI and must not be unduly stiffened as a result of applying the wetting agent.